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Date: Sun, 10 Aug 2014 16:18:13 -0700
From: Guenter Roeck <linux@roeck-us.net>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Oleg Nesterov <oleg@redhat.com>, Kees Cook <keescook@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>
Subject: Re: Runtime trouble with commit dbd952127d (seccomp: introduce writer
 locking)
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On 08/10/2014 02:10 PM, Linus Torvalds wrote:
> On Sun, Aug 10, 2014 at 1:51 PM, Guenter Roeck <linux@roeck-us.net> wrote:
>> That means that the broken configuration is (CONFIG_DEBUG_SPINLOCK=n,
>> CONFIG_SMP=n).
>> It also means that the BUG_ON checks introduced with the seccomp commit
>> will cause this configuration to fail hard at least for architectures where
>> CONFIG_SMP
>> can be disabled, and if those architectures use
>> include/linux/spinlock_types_up.h.
>
> Yes. This is why we have "assert_spin_locked()". You can't use
> BUG_ON(spin_is_locked()), and !spin_is_locked() tends to be even worse
> unless you can prove that nobody else can get the lock simultaneously.
>

git grep 'BUG_ON.*!spin_is_locked'

suggests that this may be a spreading sickness ... unless the other users
know for sure that SMP will always be configured.

What is the better fix ? Add NR_CPUS != 1 to the test, as mm does,
or remove it entirely ? Or something else ?

Guenter